zm: add new attribute 'assume_defaults' to dbus_proxy macro
This is the initial step towards reworking dbus_proxy approach
to defaults.
It introduces a new assume_defaults attribute (defaulting to
true), which reflects the status quo: currently, all generated
proxies assume (and auto-generate) some default values for path
and service. In some cases, the auto-generated values could be
wrong and misleading.
The new attribute allows to selectively disable the implicit
default.
Closes: #284 (closed)
Edited by Luca Bruno